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Lineloss,

Thanks for the tip, now more questions....

All I can say is I rotated my horizontal paired yagis each direction, at VERY graded angles (small increaments), and I did this for several heigths at 12" heigth increaments, and I did some tilting....I never really noticed any COMPLETE or near complete drop out of my #22, nor any other channel within beam width range of course...

So are you saying, even given this, I may still have wrong phasing, given my signal strengths were about the same as a single yagi? I guess to confirm you would need to have them at the exact height where the thin slice you speak would null out the signal, or is the height irrelevant...


:confused: more than ever
 

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Also I once had a bad balun: It still partially worked and that why it caused me a lot of grief. It did not phase properly either way…. But I can't see this happening to often.
Its very easy to break a balun just by overtightening it. And a lot of times, only one of the inside tiny wires break, leaving it to still "work", but poorly.
 

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:D, they were gagned side by side (1.077m),

right now I am testing them vertically stacked...

the side by side SEEMED slightly better than a single one, and SEEMED better than vertical stack, more in terms of signal stability. But very difficult to tell...
 

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Balm,

If you have done the following and are getting one main loab and no null you are in phase.. you should see a gain:

Take the time to make sure your polar plot represents your antenna exactly; make sure it is perfectly symmetrical when checking your main lobe and all your side loabs. Watch your signal strength and swing the array left to right for various channels to confirm this. With ganged XG's, incorrect phase will show up as two main loabs with a very precise null dead on.

If you have any symmetrical polar issues, you must have a poor balun, poor connection, bad combiner, (non equal rg length), dud antenna, very strong local broadcast (does not have to be UHF) or some freak reflection.... or something else I am missing. So you can do this by rotating away from a known channel broadcast tower to the left and then to the right by a certain degree increment and should record identical drop in signal strengths for each direction.

If everything is working as it should:
From the signal changes in height you have, I still think a gang with one adjustable antenna (height) has the best chance for you problem channel.

By your post I have assumed you have not missed anything simple...:D and that is leaving partially me confused as to what else this could be? :confused:

Stay focused, stay positive, don't smash stuff... The XJ dose sound like some kind of missle....but you know what happens after you launch them! :eek:
 

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balm,

Oh crap... vertical now right.... Must pay attention :eek:
Ya, just flip one antenna's balun polarity and note the before and after strength... do this with mid strenght steady state channels.

Cheers
 

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lineloss,

Not only that, mine are DIY yagis, NOT XG's and Im not sure the yagis perform the same way as do the XG (pattern). These posts are probably belonging in the another thread.

Thanks for the tips though. after reading your tips im pretty confident their phased properly, but it cant hurt to reverse one balun anyway jsu to be sure!
 

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91XG

I have a severe problem with multipath and a weak signal. I was attempting to receive the 4 UHF and 1 VHF-Hi station on Mt. Mansfield in VT.

I could receive UHF's 22, 14, and 32 without a problem. But UHF 43 was a problem.

What I did to rectify the problem was get a Research Communications Pre-amp, and I purchased a 2nd 91XG and got an additional middle boom section for both of them.

The antennas were spaced at 36" and ganged together into a CM joiner with RG11 coax. The down-line to the house is 150' of 7/8" hardline.

The math suggested a 2.5 db gain from the combining the antennas, and a possible .5 db increase from the extra boom, really making it a 3.0 db gain overall. It was just enough with the hardline, new pre-amp, and RG11 that CH 43 was stable except in hard rain/snow.

The longer 91XG is very difficult to maneuver onto a 30' antenna mast/pole. Try doing that with 2 on a horizontal boom. Take your time, don't drop the whole assembly. Once the booms are bent, they are trash.

To give the antennas support, and equal spacing for the entire length, I used little screw eyeballs on the end of 36" hardwood dowels and put those between the wingnuts and the boom on one antenna and joined it to the same location on the other antenna. Additionally, I put a 36" dowel from the front of the lower bracket to the tip of the front boom to keep the sagging down. Lots of triangles and perpendicular connections will keep everything square and straight and keep you from having a negative gain due to mis-alignment of the antennas.

There is quite a bit of weight there if you're more than a foot or two above a rotator. Get a rotor support bearing. I've already killed one CM9521a rotor even with the bearing (I had a 10' mast from the rotor and a Funke PSP.1922 5' below the 91XG's). I have since relocated the VHF-Hi antenna and shortened the height of the 91XG's above the rotor.

As far as increasing the gain, Antennas direct said with the additional boom piece, you are approaching the law of deminishing returns. 1 additional section helps, but you would need to add 4 or 5 more sections to gain another appreciable gain increase. They did mention increasing the size of the reflector, but I have not done that yet. I'll have to do more re-inforcing all around and I would need a real Ham rotor to be safe if I increased the size of the reflector.

I have a deep fringe reception thread over at TVFool with all the details if you want more info. I'm subscribing to this so ask me any questions here as well.

~ryan
 

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b1gmoose,


Hi there, pretty extreme stuff :eek:

1. where are you located

2. what do you think was the SINGLE biggest change improving reception and what pre-amp did you use before...

3. Can you post ANY pics...

4. did you get a better deal on all those booms from Antennas Direct....

5. How, who, did you decide on 36" separation..

thanks
 

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I'm located in Passumpsic, VT. I live at approx 500' elevation with a river going through the back yard. Narrow valley, hills on the east and west at 1000'+-. Lots of metal roofs, lots of power lines, lots of interference/multipath with how the signals bounce around.

I had a CM7777 Pre-amp before and RG11 to the house. The extra booms were no charge and shipped free from antennas direct.

No pics for now. The setup is coming down as I'm moving to a much better reception area within the next 2 months. But the gear might be overkill :-( .... but I might have some good chances at DX'ing.

36" was decided upon as that was the length of the wooden dowels that I had. I had tried 40" +- and I just could not keep the antennas square to each other for a long period of time.

Single biggest change was probably the pre-amp. That smothed out the signals across the board for all channels. The hardline reduced the attenuation that I would have had if I kept the RG11 or if I only used RG6.

Stacking the antennas together side by side, made a huge improvement as far as the multipath interference.

It was sort of a package deal for me, everything helped, but it's a complete system that won't work very well without the other components.

~ryan
 

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Discussion Starter #72
Moving to get better OTA - Oh Ya!

Maybe not the first reason of why you are moving- but I love the connection.

What's that place in South Carolina for the best OTA - Mt. Mitchell?

What about Mt. Washington in VT?

Cheers!

:cool:
 

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b1gmoose,

Lots of metal roofs, lots of power lines, lots of interference/multipath with how the signals bounce around.
what exactly was happening on the digital, and analog channels...
 

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I have no idea exactly why or what was happening to the radiowaves. Take UHF 18, Strong transmitter 14.5 miles away. I could receive a 100% digital lock with it and a standard unamplified 91XG no matter which direction it was pointed. A full 360 degrees of reception from that station.

Analog stations had lots of TVI on them. Ghosting even when pointed dead on or off to the sides of the transmitters. Even receiving VHF 7, 9 or 11 from Canada was a challange.

MT Washington, NH won't be visable from where I'm noving. I'll be at about 1200' on the side of a hill. The hill top is at 2200', so there will be no channels from the east. But North, South, and West, I'll be golden. West might be a little tricky though as Mt. Ellen (Suggarbush) is right there, but S. West will be fine.
 

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Anyways, sorry to hijack the thread, back to extending the 91XG's.

I think alone, a longer 91XG may help if there is a station that comes in at night, but drops out during the day. For those on the edge of the digital cliff, it may work.

The next level is to horizontally or vertically stack 2 longer 91XG's with larger reflectors.

Stage 3 (like turbo's and stuff for cars) would be to go all out, 7/8" hardline (or 1.5" hardline if you can get it) and a quality pre-amp. I like the Research Communications system, it was around $180 shipped with the currency conversion last year. Or at least a CM7777 or equivelent.

Don't forget, if you have a long run of hardline, such as 1/2" or 7/8" or whatever, if you are receiving a VHF-Lo, you may have to worry about the slope because it will attenuate less than a UHF station over long run (over 100 or over 300').

~ryan
 

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b1gmoose


what did antennas direct say about changing the reflector...to larger...
From antennas direct:
Ryan,

Below is the response from our engineer. I hope this helps somewhat:





I'm afraid that while I've done some computer simulations of the stock 91XG I have not investigated any design modifications such as additional boom sections, larger reflectors, stacking etc so I can't offer any really solid engineering advice on performance optimizations using such methods. I can offer some general suggestions however.



For those stacking antennas for added gain it is important to use a high quality combiner with identical cable runs between each antenna. Having the same length is very important to ensure that the signals are added in phase.



For those adding additional boom length, there is a law of diminishing returns and there's probably little to be gained by adding more than one additional boom section.



The same law of diminishing returns also applies to the reflector. Here however I would suggest that the larger reflector will enhance front to back ratio more than forward gain.



It’s important to allow some space between the VHF antenna and the UHF antennas so that they do not couple and detune and distort patterns.

The exact spacing will vary depending on the antennas under consideration. As a rule of thumb I'd try to get the VHF antennas at least a couple of feet away from the VHF. The 91XG is quite large however and more may be required to keep from degrading the VHF antenna.



As for the amplifier, I have tested the channel master series and I believe that our PA19 is a superior amplifier in terms of noise as well as resistance to overload. If there were one thing that I would change out it would be the amplifier. Even if they are in the deep fringe for TV, there is a real possibility that they are close to a cell tower or other source of interference that can effectively desensitize the receiver to weak TV signals.





Have a great Thanksgiving,

Noel
In another email from antennas direct, they also indicated that they have not compiled any windload data for the 91XG.
 

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91XG - bend directors = more gain?

I am wondering if bending the directors towards the transmission towers on a 91XG will improve gain as it does on mclapp's designs and the SBGH curved mesh?
 
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